1. Technical Field
The present disclosure relates to methods for making field emitters and, particularly, to a method for making a carbon nanotube field emitter.
2. Description of Related Art
Carbon nanotube has excellent electrical and mechanical properties. The carbon nanotube can transmit extremely high current density and emit electrons easily at low voltages. Thus it can be used as a field emitter in a variety of display devices, such as field emission display devices.
The two main methods for making a carbon nanotube field emitter are the in-situ synthesis method and the printing method.
An in-situ synthesis method is performed by coating metal catalysts on a conductive cathode electrode and directly growing carbon nanotubes on the conductive cathode electrode by chemical vapor deposition. However, the carbon nanotubes synthesized on the cathode electrode are inevitably entangled with each other. Thus, the field emission characteristics of the carbon nanotubes are generally unsatisfactory. Furthermore, the carbon nanotube field emitter has relatively low mechanical properties.
A printing method is performed by printing a pattern on a conductive cathode electrode using carbon nanotube based conductive paste or organic binder. The carbon nanotubes can extrude from the pattern to form emitters by a series of treating processes. However, the density of the effective carbon nanotube emitters is relatively low, and the carbon nanotubes are easily entangled with each other and are oblique to the conductive cathode electrode. Furthermore, the treating processes may include a step of peeling the paste off to form extrusions of the carbon nanotubes. Such peeling step may damage the carbon nanotubes and/or decrease their performance. Thus, the efficiency of the carbon nanotube field emitter obtained by the printing method is relatively low, and controllability of the printing method is often less than desired. What is needed, therefore, is to provide a method for making carbon nanotube field emitters, in which the carbon nanotube field emitter has stable field emission performance and high mechanical properties, and the method can be utilized easily.